The U.S. Justice Department argues a warrant is not needed even if future "scientific enhancements" or an aggregation of devices is used.
GPS provides the location of a device and the timing of its movements anywhere on the globe, even in bad weather, as long as the device is able to fix on four or more GPS satellites in orbits maintained by the U.S. government.
The system has many uses in the private sector, such as the determining the locations of hikers or campers and the flights of commercial airlines or routes of ships. Its military uses for warplanes, warships and missiles are obvious.
Its use among law enforcement is widespread, the administration says.
But can law enforcement use the technology without a warrant in a constitutional way?
The American Civil Liberties Union, which filed briefs in the GPS case in the lower courts, says it can't. GPS technology is just too "invasive" to be used without a warrant.
"To explain why GPS tracking is invasive, particularly over long stretches of time," the ACLU said, "it's hard to do better than these words from a Washington, D.C., federal appeals court decision:
"'A person who knows all of another's travels can deduce whether he is a weekly churchgoer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups -- and not just one such fact about a person, but all such facts.'"
In 2004, a joint Safe Streets Task Force of the FBI and the Metropolitan Police Department set out to learn the "facts" about Antoine Jones, who owned and operated a nightclub in the District of Columbia and was suspected of narcotics violations.
Agents used a variety of techniques designed to link Jones to his alleged co-conspirators and to suspected stash locations for illegal drugs. In addition, agents obtained a warrant from a federal judge in Washington authorizing them to secretly install and monitor a GPS tracking device on Jones' Jeep Grand Cherokee -- as long as it was installed within 10 days and only within the District of Columbia.
But the agents did not install the device until 11 days after the warrant was issued, and while the Jeep was parked in a public parking lot in Maryland, not the district.
Despite this legal problem, the battery-powered GPS device worked. It communicated with satellites to establish the Jeep's location, accurate within 50 to 100 feet. It generated data only when the Jeep was moving -- the device was in "sleeping" mode when the vehicle was stationary to conserve battery power.
Court records said the device enabled agents to track the Jeep to the vicinity of a suspected drug stash house in Fort Washington, Md., which confirmed other evidence of Jones driving his vehicle to and from that location.
Investigators heard on intercepted calls that Jones was expecting a sizable shipment of cocaine in late October 2005, court records said, and executed search warrants at various locations.
They recovered nearly $70,000 from Jones' Jeep, and recovered wholesale quantities of cocaine, thousands of dollars in cash, firearms, digital scales and other drug-packaging paraphernalia from his suspected customers.
At the stash house in Fort Washington, agents recovered approximately 97 kilograms of powder cocaine, almost one kilogram of crack cocaine, approximately $850,000 in cash and various items used to process and package narcotics, court records said.
Jones was indicted for allegedly conspiring to distribute 5 kilograms or more of cocaine and 50 grams or more of cocaine base, and 29 counts of using a communications facility to facilitate a drug-trafficking offense.
Before trial, Jones' lawyers moved to suppress the data from the GPS tracking device. A federal judge ruled that any information gleaned while the Jeep was on public roads was admissible, but any data obtained while the Jeep was in Jones' garage was not.
The jury acquitted Jones of some charges and was unable to reach a verdict on others.
Then a new federal grand jury, in a superseding indictment, charged Jones with a single count of conspiracy to distribute and possess 5 kilograms of cocaine and 50 grams or more of cocaine base.
After a second trial in which prosecutors used GPS information obtained while the Jeep was moving, Jones was convicted of the sole count. A judge sentenced him to life in prison and ordered him to forfeit $1 million in proceeds from drug trafficking.
But the U.S. Court of Appeals for the District of Columbia, sometimes called the second most important court in the United States, reversed the conviction.
An appeals court panel conceded that the Supreme Court said in 1983's U.S. vs. Knotts when police placed a beeper inside a container of chemicals in order to track it, it was not a search within the meaning of the Fourth Amendment because someone "traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another."
The Fourth Amendment says, "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
But the courts have also said the Fourth Amendment's protections extend only to places where there is a "reasonable expectation of privacy" -- not in places such as airports, for example, where passengers are searched before boarding an airplane.
The Washington appeals court said Knotts was not the controlling precedent, because officers in that case monitored a "discrete journey" of 100 miles, where in the Jones case police were conducting monitoring of a vehicle over several weeks.
The Knotts ruling also "reserved" -- did not answer -- whether a warrant would be required before police could use electronic devices as part of a "dragnet-type law enforcement," such as "24-four hour surveillance."
The appeals court also conceded that two other U.S. courts of appeal in different circuits have ruled that prolonged GPS monitoring without a warrant did not violate the Fourth Amendment.
The appeals court said Jones has a reasonable expectation of privacy in the public movements of his Jeep over the course of a month, because he had not exposed the "totality" of those movements to the public -- "the whole of a person's movements over the course of a month is not actually exposed to the public because the likelihood a stranger would observe all those movements is essentially nil."
The appeals court also concluded that a reasonable person "does not expect anyone to monitor and retain a record of every time he drives his car, rather, he expects each of those movements to remain disconnected and anonymous."
Moreover, seven states have enacted laws requiring the government to obtain a warrant before using GPS technology, the appeals court said.
The appeals court also rejected the government's argument that the "automobile exception" to the Fourth Amendment's warrant requirement -- generally used in traffic stops -- saying "the automobile exception permits the police to search a car without a warrant if they have reason to believe it contains contraband; the exception does not authorize them to install a tracking device on a car without the approval of a neutral magistrate."
After the panel's ruling, the administration asked the full appeals court to hear the case, but was rejected.
The Obama administration then asked the U.S. Supreme Court for review.
After pointing out the conflict in rulings by several appeals courts, the administration's petition says: "Prompt resolution of this conflict is critically important to law enforcement efforts throughout the United States. The court of appeals' decision seriously impedes the government's use of GPS devices at the beginning stages of an investigation when officers are gathering evidence to establish probable cause and provides no guidance on the circumstances under which officers must obtain a warrant before placing a GPS device on a vehicle."
The petition warns the confusion could spread, tacitly acknowledging the Washington appeals court frequently sets the tone for other appeals courts throughout the country.
"Given the potential application of the court of appeals' 'aggregation' theory to other, non-GPS forms of surveillance, this (Supreme) Court's intervention is also necessary to preserve the government's ability to collect public information during criminal investigations without fear that the evidence will later be suppressed because the investigation revealed 'too much' about a person's private life."
The petition added: "This (Supreme) Court has held (in Knotts) that a 'search' within the meaning of the Fourth Amendment occurs only where a 'legitimate expectation of privacy' has been invaded by government action. ... As a result, 'what someone 'knowingly exposes to the public is not a subject of Fourth Amendment protection.'"
The Supreme Court should decide soon whether to grant the government's petition for review. The justices are scheduled to consider it in conference Thursday.